The pages of a respected climate change journal are not a place one would expect to find a bad-tempered exchange over the merits of iconic soft drinks. Yet such a disagreement -- over the rates at which Coca-Cola and Brazilian guaraná lose their fizz -- was recently covered in the normally decorous pages of Climatic Change. While the immediate topic seems inconsequential to say the least, the larger context is of major importance -- do tropical hydropower reservoirs cause greenhouse gas emissions to match those from fossil fuel plants?